1. Field of the Invention
This invention relates to rotating machinery and more particularly to determining torque in rotating machinery.
2. Related Art
In the ever-increasing competition in the industrial field, industrial equipment, such as rotating machinery, must operate at or near full capacity and sustain such operation for long periods of time. With this type of demand placed on such equipment, periodic maintenance to avoid a catastrophic failure becomes important. Of course, periodic preventative maintenance requires that the equipment be taken off-line for service, thereby potentially resulting in unnecessary down time. Maintenance engineers have been challenged to establish proper time intervals for scheduled preventative maintenance in order to reduce such unnecessary down time.
Alternatively, some maintenance engineers have concluded that the equipment should operate until catastrophic failure. This stems from the fact that, in some instances, it may be better to operate equipment until it fails than to accept the maintenance and the resulting penalty costs of shutting down the equipment prematurely. Also in lieu of scheduled maintenance, some defects may be found by a trained operator. Because such detection is subject to human interpretation, pass/fail criteria may vary between operators and also from day to day with the same operator. Other defects may not be detected at all.
Attempts have been made to automatically monitor such equipment for defects through the use of a sensing element disposed within the equipment itself or through the use of a hand-held device which is periodically attached to one or more discrete locations.on the machine being monitored. More sophisticated monitoring systems are permanently installed and carry out essentially continuous monitoring of a machine-mounted transducer along with computer-based analysis of all monitored data.
Most automatic monitoring systems typically sense vibration or temperature. Vibration is produced by the moving parts in the rotating machinery due to causes such as unbalance, misalignment of shafts, worn out bearings, broken gear teeth or foreign particles lodged within the machine. Excessive levels of vibration indicate malfunction of the machine, which can result in machine failure. The temperature of a bearing, for example, can also be monitored to detect the occurrence of over-heating. In some instances, the oil level in the machine may be monitored, automatically through the use of a float system or manually through the use of a dipstick or a sight glass, so that the likelihood of defects or malfunction of the device due to low oil level may be reduced. Other automatic means to detect oil level include beam techniques that measure time of flight or frequency modulation of an ultrasonic, microwave or light/laser beam. Electrical methods have also been employed that detect changes in current, voltage, capacitance or inductance of the liquid to determine the fluid level.
In addition to the above-mentioned parameters sensed by conventional monitoring systems, the torque applied to the shaft of the machine may also be sensed, which may indicate whether machine is being overloaded. Typically, this requires the use of expensive and complicated measurement devices, such as strain gauges, positioned at discrete points on the rotating shaft.
According to one aspect of the invention, torque information of a rotating machine may be determined by counting a number of discrete samples representing a rotation of a rotating component. If the number of discrete samples representing the rotation of the rotating component changes, it may be assumed that the torque has changed due to a change in loading placed on the rotating machine. The amount of change in torque may be determined by determining the amount of change in the number of discrete samples representing the rotation of the rotating component.
In one embodiment, a sensor to sense the rotation of the rotating component and an analog-to-digital converter communicating with the sensor are provided. The sensor is sampled with the analog-to-digital converter to generate the number of sample readings.
In another embodiment, a plurality of a number of sample readings between complete revolutions is counted and minimum, maximum and mean number of sample readings between complete revolutions are calculated. The torque is based on the mean number of sample readings between complete revolutions.
In yet another embodiment, the torque of another rotating component is determined by comparing the determined torque to an efficiency of the device.
In another embodiment the rotating component is an input shaft and the other rotating component is an output shaft.
In another aspect of the invention, the above method may be performed by an apparatus or a system.